In carrying out homogeneous polymerizations with typical monomers, the reactive sites on the separate monomer molecules are located relatively far from each other. Consequently, in order for the polymerization reaction to proceed, the monomer molecules must be sufficiently mobile within the reaction mixture so that they can diffuse to locations that bring the reactive sites into contact with each other. Unfortunately, as the polymerization reaction proceeds, the glass transition temperature, T.sub.g, of the forming polymer rises as the conversion increases, reducing the rate of diffusion of the monomer molecules within the mixture, and slowing the polymerization as a result. Consequently, it is impossible to obtain a high T.sub.g polymer by polymerizing monomeric materials in an isotropic state at low temperatures because of the inhibiting influence of the rising T.sub.g. Stating the effect differently, when molecular diffusion ceases, a polymerization reaction is no longer possible, seriously limiting the degree of reaction completion that can be achieved with homogeneous polymerizations. Since it is necessary to increase the reaction temperature during the polymerization to maintain a practical rate of diffusion, it is impossible to achieve substantial polymerizations at low temperature.
By way of contrast, where the reaction sites of the monomer molecules in heterogeneous polymerizations can be maintained in spatially adjacent positions, relatively complete reactions can be obtained even in substantially molecularly immobile systems. Consequently, heterogeneous polymerization systems in which the reacting monomers are structured to possess ordering moieties or segments, offer the possibility of obtaining polymerizations yielding polymers with substantial glass transition temperatures, in relatively complete conversions. This is true even at reactive temperatures substantially below the resulting polymers' glass transition temperatures, since it is unnecessary to promote molecular diffusion by heating the reaction mixtures.
Liquid crystalline and crystalline materials contain such ordering segments in the form of rigid portions, termed "mesogens". Such materials are capable of molecular ordering, including nematic and smectic ordering, in which the molecules arrange themselves in heterogeneous adjacent, molecular configurations wherein the molecules are aligned in parallel relationship to each other.
Thermotropic liquid crystalline monomers and polymers have been intensely studied during recent years, the primary interest up to the present time being the temperature ranges in which liquid crystalline formations can be observed, as well as the relaxation times, or "creep" rates shown by the materials. Difunctional vinyl monomers which exhibit liquid crystalline behavior have, for example, been synthesized and heterogeneously polymerized to form cross-linked polymers by Strzelecki et al, Bull. Chem. Soc. de France 2,597,603,605 (1973). The resulting polymers thus produced, however, are brittle, crystalline materials, lacking the "toughness" required for products capable of widespread application.
Various other organized or liquid crystalline systems which, however, possess a single functional group, have also been employed. For example, styrene- sulfonic acid organized by reaction with ionenes has yielded cationic polymers in reactions displaying appreciable rate enhancements over those of homogeneous monomers at the same concentration. Ionenes have also been used in the past by Tsuchida et al., J. Polymer Sci. 13, 559 (1975), to increase the rates of methacrylic and acrylic acid polymerizations. Konstantinov et al., Vysokomol. Soed., 9A 2236 (1967) has polymerized methacrylyl oxybenzoic in the liquid crystalline state at higher rates, than those obtained in the isotropic state. Cholesteric liquid crystalline monomers, e.g., cholestryl methacrylate, have been polymerized by Saki et al., Polymer J., 3, 414 (1972), at rates considerably more rapid than those obtained during the polymerization of such materials in the isotropic state at even higher temperatures. The polymerization of monofunctional monomers, however, yields polymers with large side chains; consequently, polymers so produced tend to yield high T.sub.g, brittle materials, again limiting their usefulness.